As one of the most impressively menacing creatures to have ever walked the earth, the Tyrannosaurus rex has been mercilessly teased for its disproportionately tiny arms. Reasons for why the T. rex evolved to have such tiny forelimbs remain one of the biggest mysteries in paleontology.
Darwinian logic supposes that a trait that persists through generations must somehow be beneficial, or at least not detrimental. Was this the case for the T-rex? For example, did these structures shorten over time because the T. rex's great big teeth were enough, and bulky arms just got in the way? Or perhaps the T-rex never had use of their arms to begin with, and these unused structures evolved to be less conspicuous over time.
Paleontologists hope to find the answer to this most perplexing question by studying the arm bone of SUE, the most famous T. rex in history. In particular, they hope that detailed scans of the skeleton, taken with X-rays from the Advanced Photon Source at the US Department of Energy's Argonne National Laboratory, will reveal clues about how this terrifying creature used its arms.